1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices and, more particularly to a method of manufacturing thin film gate insulated field effect transistors consisting of polycrystalline semiconductor films.
2. Description of the Prior Art
The prior art includes methods utilizing low pressure CVD by which polycrystalline semiconductor thin films are deposited at temperatures ranging from 550° C. to 900° C. Recently, along with development of liquid crystal panels having wide display area, there have been needs for the deposition technique to coat polycrystalline semiconductor films over with areas of substrates.
Polycrystalline films are formed by depositing amorphous semiconductor films by low pressure CVD and then recrystallizing the amorphous films since direct deposition of polycrystalline films on wide areas is difficult for the reason of reaction temperature. On the other hand, it is very difficult to deposit uniform semiconductor films by low pressure CVD. This is the problem also in the case of plasma CVD which, requires longer deposition times.
Sputtering on the other hand is excellent in this sense. Particularly, there are following advantages when films are deposited by magnetron sputtering.
1) The surfaces of substrates are less damaged by high energy electrons since the electrons are confined in the vicinity of the target.
2) Wide areas can be coated at lower temperatures.
3) No dangerous gas is used so that safety process and practicability are ensured.
The sputtering is carried out without hydrogen doping because the electric characteristics of hydrogenated amorphous semiconductors deposited by sputtering are not so good as to satisfy requirements of channel formation for transistors. The semiconductor films deposited by the sputtering, however, have a disadvantage that thermal crystallization thereof is very difficult.